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Dk. Cunningham—Surface Anatomy of the Primate Cerebrum. 249

of Rolando, and takes an oblique course upwards and forwards towards the
lower end of the sulcus prsecentralis inferior (fig. 53, i. t.). As we have
already noted in Chapter III., the partial union of the fissure of Rolando
with this furrow leads, in many cases, to a superficial connexion between
the former and the fissure of Sylvius. In other cases, however, where the
inferior transverse furrow is strongly developed, and, perhaps, placed somewhat
further forward than usual, it may open above into the sulcus prsecen-
tralis inferior, and carry it downwards into the Sylvian fissure. When
this occurs the point of junction between the inferior transverse furrow and
the inferior prsecentral sulcus is always marked by a deep annectant gyrus.
It is interesting to observe that, in cases where the inferior transverse
furrow is strongly developed, it is usual to find the vertical limb of the
sulcus prsecentralis inferior shortened. Eberstaller has also noted this. He
says : " An manchen Gehirnen konnte ich auch beobachten, dass eine
stark entwickelte c. t. r. (». e. inferior transverse furrow), gleichzeitig mit
rudimentarer Ausbildung des unteren Abschnittes der Pracentralfurche sich
vorfand, also gewissermassen die eine die andere in ihrer Ausbildung
behinderte, beziehungsweise compensirte."*

The sulcus cliagonalis of Eberstaller is placed in front of the inferior
prsecentral fissure, and divides the pars basilaris of the inferior frontal
convolution into two triangular fields (fig. 53, s. d.). Its lower end, as a
rule, opens into the posterior horizontal or the anterior ascending limb
of the Sylvian fissure. From this it ascends obliquely upwards and backwards
towards the inferior prsecentral sulcus. Sometimes it opens into
this, and then a communication between the prsecentral sulcus and the
Sylvian fissure is the result. A deep annectant gyrus invariably marks its
point of junction with the former.

An examination of fifty adult hemispheres, with the view of determining
the frequency of the communication between the inferior prsecentral sulcus
and the fissure of Sylvius has afforded the following results:—

1. In 58 per cent, the lower end of the inferior prsecentral was free, and
in no way connected with either the inferior transverse furrow of the fissure
of Rolando or the sulcus diagonalis.

* Das Stirnhirn, p. 62. Leipzig, 1890.

ROYAL IRISH ACADEMY.-CUNNINGHAM MEMOIRS, NO. VII. [32]